Communication theory: Improved OFDMA uplink transmission via cooperative relaying in the presence of frequency offsets-Part I: Ergodic information rate analysis

In this two-part paper, we evaluate ergodic and outage information rates in an orthogonal frequency-division multiple access (OFDMA) uplink with amplify-and-forward (AF) and decode-and-forward (DF) relays in the presence of frequency offsets. Each node plays the roles of the source node and the relay, simultaneously, but on different subcarriers. In Part I, the ergodic information rate is derived, and in Part II, the outage information rate of the considered scheme is derived. For a given frequency offset, unlike that of the AF mode, the DF ergodic information rate does not monotonically increase with α (the ratio between the power allocated to the source node and the total transmit power), and 0 < α < 1 can be optimised to maximise the ergodic information rate. Numerical results show that AF cooperation does not outperform the conventional transmission (without relaying) with regard to ergodic information rate. In contrast, with DF relaying, performance gains are possible.